Insulating oil compositions



Patented Oct. 7, 1941 UNITED STATES PATENT oFsicE Charles E. Tralitman, East McKeesport,

to Gulf Research & Development Coma corporation of Delasignor Dany, Pittsburgh, Pa.,

ware

Pa., as-

No Drawing. Application March 22, 1940, Serial No. 325,479

4 Claims; ((1252-63) This invention or discovery relates to insulating oil compositions; and it comprises such a composition, particularly. a transformer oil, highly resistant to deterioration by oxidation and including a petroleum 011 containing a small amount of an aniline derivative selected from the class consisting of benzyl-peanisidi'ne and "benzyl-p-ph'enetidine; all as more fully hereinafter set forth and as claimed.

In many types of electrical transformers the ,core and windings are immersed in a suitable petroleum oil, for serving as a dielectric and for carrying heat away from the core and windings. The requirements of a transformer oil include good dielectric properties, low viscosity to facilitate heat transfer for convection, low pour point to avoid solidification of the oil by cold, high flash and fire points to minimize danger of fire and explosion and low volatility to reduce evaporation losses. in addition the oil must be re- 2G sistant to oxidation, and must be of such character'as to resist emulsification with water.

Transformer oils ordinarily are distillate oils refined in'such manner as to secure the specified characteristics to as great an extent as possible.

Achievement of satisfactory oxidation resistance is diflicult, for while oxidational changes are slow, transformer oils are ordinarily expected to remain in service .over long periods. Oxidational changes result in the formation of insoluble matter or sludge. The sludge tends to render the oil more miscible with water, with production D of emulsions in the esence of condensed water and a consequent degradation of the dielectric to form a definite amount of sludge, say 0.1 per cent lv weight of the oil.

I have discovered an-anti-oxidant which brings about both a marked lengthening of the induction period and a lessening of the rate ofsludge dormatlon, when incorporated in transformer oils even in minimal amounts. The anti-oxidant has certain other advantages. It is quite soluble in 011, more so than many other anti-oxidants, but is highly insoluble in water, thereby minimizing the tendency to formation of aqueous emulsions.

In the best embodiment of the invention the antioxidant is a compound which can be represented by the structural formula in conjunction with other anti-oxidants but it is properties of the oil body. The sludge also deposits on the windings and core with reduction of the efilciency of heat transfer. Oxidation of transformer oils'tends to be promoted by contact with metals, especially copper, and with the usual varnishesand insulating materials.

Various materials have been proposed for incorporation intotransiormer oils with the object of inhibiting oxidation, and some of these have come into use. The usual anti-oxidants may be divided in two principleclasses: (1) those which are associated with a lengthening oftthe induction period, that .is the time whichelapses before appearance of sludge iirthe oil subject to oxidation, and (2) those which reduce the amount 60 of sludge formed per day after it once begins to form.

takes into account -both' these characteristics, viz., the time required, under the test conditions,

so effective, both as regards prolongingthe induction period and minimizing the rate of sludge formation, as to render addition of other types of anti-oxidants unnecessary. When very small proportions of my antioxidant are used in the oil, it is sometimes convenient to incorporate a little of certain alleviation products of phenols and substituted phenols in which there are present alkylatior; linkages of secondary or tertiary 40 type, and exemplified byv the compounds;

In evaluating oils containing anti-oxidants, the most useful criterionris a value which 2,6-di-tertiary-butyl-i-methyl phenol 2,6-di-tertiary-butyl-4-ethyl phenol 2,6-di-tertiary-butyl-4-cyclohexyl phenol I 2,6-di-tertiary-butyl-4-benzyl phenol 2,4,6-tri-tertiary-butyl phenol 2,6-di-tertiary amyl-4-methyl phenol In the following table, comparative oxidation test results are set forth for oils containing the new anti-oxidant, for an untreated oil, and for certain other anti-oxidants not part of the invention. The test data were obtained in ac-' cordance with the sludge formation test for mineral transformer oil, described by F. M. Clark and E. A. Snyder in their paper entitled Testing for Sludge Formation in Mineral Transformer '11 presented at the Thirty-ninth Annus! Meeting -Ior the American Society for Testing Materials. The test procedure described in the aforesaid paper was developed in collaboration with the laboratories of a considerable number of firms engaged in oil refining and in the manufacture of electrical equipment.

In this test, samples of oil are maintained in tubes containing copper wire at a constant temperature of approximately 120 C. The tubes are open at the top to an enclosed air space and dry air is passed at a controlled rate of 1 /2 to 2 cubic feet per hour through the enclosed space above the sample tubes. Into each tube is introduced 22 grams of oil or oil composition to be tested, a number of tubes being employed. At prescribed intervals the tubes are successively removed and the amount of sludge determined. The results of these tests are reported in terms of the induction period, the per cent of sludge formed per day and the total number of days taken to form 0.1 per cent of sludge.

The oil employed in all of the tests set forth hereinbelow was a typical petroleum transformer oil, commonly used for the purpose indicated.

Transformer oil sludge formation test carried out at 120 C. in the presence of copper tions contemplated in the invention and tests '7 to 13 relate to compositions not a part of the present invention. As indicated by tests- 2, 3 and 4, the benefits obtained with benzyl-p-anisidine increase with proportions thereof up to around 0.3 per cent, while in most cases further increase does not further reduce the oxidation sensitivity of the oil. By using a very small proportion of benzyl-p-anisidine, together with an addition of 2, 6-di-tertiary-butyl-i-methyl phenol, far better results are obtained than would be expected from a consideration of the effect of either anti-oxidant alone in the stated proportions; cf. tests 2, 5 and 7. Benzyl-panisidine gives much better results than do other compounds of the same general class, some of which, like di-benzyl-p-anisidine have little or no efiect on oxygen stability of the oil; cf. tests 1 and 9.

While my invention has been described herein with particular reference to, transformer oil compositions, benzyl-p-anisidine and benzyl-pphenetidine are equally effective anti-oxidants in other forms of electrical insulating oils, and insulating oils generally containing stabilizing amounts.of these compounds are included within Rate of sludge for- Test Inducmation, in Time to No Inhibitor tion 0.01% per form 0.1% period day, after sludge induction period Days Days 1....... None 0 1.13 2 Benzyl-p-amsidlne 0.1%- 3 0.75 17 3 Ditto 0.3% 5 0. 18 60 or more 4 Ditto 0 5 0.18 60 or more 5 Ditto 0.1% plus 2,6- di-tertiary butylmethyl phenol 0.3%... 5 0. 18 60 or more 6 Benzyl-p-anisidine 0.3%

plus 2,6-di-tertiarybutyl-i-methyl phenol 0.3% 5 0. 18 60 or more 7 2,6-di-tertiary-butyl-4-.

methyl phenol 0.3%... 10 2. 14 8.... Monobenzyl-p-aminophenol (satd) 0.03%... 0 0. 35 28 9 Dibenzyl-p-anisidine 0.3%. 1 1.18 5 l0 Acetyl-p-amsidine, saturated (less than 0.3%). 0 l. 25 5 p-Anisidine 0.3% 0 1.25 6 p-Phenetidine 0.3%. 0 4. (I) 3 Benzyl aniline 0.3%..--. 2 1.00 11 the scope of my invention.

What I claim is:

1. An electrical insulating oil composition comprising a petroleum oil and a small amount of an aniline derivative selected from the class consisting of benzyl-p-anisidine and benzyl-pphenetidine, dissolved in the oil.

2. A transformer oil composition comprising a transformer oil and a small amount of'a dissolved compound represented by the structural formula wherein R is selected from the class consisting of methoxy and ethoiw groups.

3. The composition of claim 1 wherein the aniline derivative is present in amount approximately 0.5 to 0.5 per cent by weight on the oil.

4. The composition of claim 1 comprising in addition a small amount of a substituted alkyl phenol selected from the class consisting of secondary and tertiary alkyl phenols and adapted to lengthen the induction period for oxidational changes in transformer oils.

CHARLES E. TRAUTMAN.

CERTIFICATE ,OF CORRECTION Patent No .2, 257 ,8 69

October 7, 19in.

CHARLES E. TRAUTMAN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring eorrectionas follows: Page 2,

sec-

0nd column, line 14.8, claim 3,.fbr "0.5 to 0.5" read --0.05'to O.-5--; and

-that the said-Letters Patent should be read with this correction therein that the same may conform bottle record of the case inthe Patent Office.

Signed and'sea led this 11th .day of November, 'A. 'D. 19LLl. I

(Seal) Henry Van lirsdale Acting Com is si oner of Patents CERTIFICATE "OF CORRECTION. Ratent No.. 2 ,257,8 69. October 7, 1911.1.

' cmrmss E. TRAU'IHAN.

It is hereby 'eer'tified thet error appears in the printed specification or-the above numbered patent requiring correction-as follows: Page 2, second colusm, line hB;, claim 3,. rei- "o. to 0.5" read --o.0 to o and that the eaid -Lattezps Patent should. be read 'with this correction therein that the seine may conform to'the reoor d of the case in the Patent Office.

' sig ed and sealed this 11th .day or nevemberjA. -D. 19h1' Henry Van Arsdale,

(Seed) Actihg Comnis sioner of Patents 

